3 Patch Quarter
Square Triangles Tutorial

Make a 3 patch quarter square triangle from half square triangles. Use the formula, or size chart, and see a video to make your own!

non-mirror image 3 patch quarter square triangles

In Lesson 1 we learned to make QSTs as hourglass quilt blocks. We used two different contrasting fabrics and made two half square triangles to make our QSTs.

In Lesson 2 we learned to make Mirror Image QSTs where 2 of the 4 half QSTs are the same.

Lesson 3: 3 Patch QSTs

Here, in Lesson 3 we will learn how to make Non-Mirror Image 3 Patch QSTs (also called split QSTs). All four of the half quarter square triangles will be the same.

Triangles 1 and 2 will be small and the same size. Triangle 3 will be twice their size.

3 Patch Quarter Square Triangle Formula

The formula for a QST is to add 1 1/4 inches to the finished size of the QST unit. Make the unit and then trim up the edges, cutting off the dog ears.

3 Patch Quarter Square Triangle Size =

Unit Finished Size + 1 1/4 inches

Adding 1 1/4 inches results in very little fabric waste. However, your stitching needs to be a very accurate 1/4 inch seam, which leaves little room for error.

Beginners may want to add 1 1/2 inches instead. Then, trim the excess fabric.

3 Patch Quarter Square Triangle Chart

This chart includes common sizes for Three Patch QSTs. The math has been done for you!

Here's how to read the above chart:

1. Locate the Finished Size (A) of the QSTs you want to make.
2. Cut 2 squares either 1 1/4 (B) or 1 1/2 (C) inches larger than that in Fabrics A and B to make HSTs.
3. From Fabric C, cut 2 squares (D) the same size as those used to make the HSTs. These will be cut in half diagonally from corner to corner to make 4 large triangles.
4. Trim the split QSTs using the corresponding Ruler Lines (E) to square them to their Unfinished Size (F).

Three Patch Quarter Square Triangle  Instructions

• All seams are 1/4 inch unless otherwise noted.
• Fabric A (print)
• Fabric B (purple solid)
• Fabric C (green solid)

Step 1 Cut Squares First, use the math chart above to locate the finished size of your QSTs (Column A).

From Fabric A cut 1 square and from Fabric B cut 1 square in the size noted in Column B (1 1/4 inch larger than finished size) or Column C (1 1/2 inch larger than finished size).

Next, from Fabric C cut 2 more squares the same size (Column D).

Step 1a Mark Top Square Place one Fabric A square right side up and place one Fabric B square right side down on top of it.

On the top square, place the mid-line marks of a quarter inch seam marker diagonally from corner to corner and with a pencil draw a line on both sides of the quarter inch seam marker.

Repeat for the second corner to corner.

Here are the two squares from Fabric A and Fabric B placed right sides together and 1/2 inch apart seam lines marked.

Step 2 Take the squares to the sewing machine. Orient the squares so that they will go under the needle on point (diagonally) and along the right side marked line.

Step 2a You can see the red stitching line. The blue lines indicate the stitching direction. The pencil dot indicates the top of the square, where I started stitching. You don't have to mark one on your square. It's there as a reference to make later instructions more clear.

Stitch along the right marked line until you are half way past the top intersecting line. Stop stitching. Lift up the presser foot.

Pivot the fabric counterclockwise by 90 degrees. Lower the presser foot.

Stitch the 1/2 inch distance to the next line. Stop stitching. Lift up the presser foot.

Pivot the fabric clockwise by 90 degrees. Lower the presser foot. Stitch along the left line to its end and off the fabric.

Step 2b Now, repeat Step 2a above to make the second stitching line. It should intersect with the first stitching line near the middle of the block.

Orient the squares on point (diagonally) so that the two lines that have not been sewn will go under the needle. Start stitching on the line to the right.

See the pencil dot mentioned in the previous step?... It is to the left and the lines on either side of it are now oriented horizontally.

Step 3 Using a rotary cutter and quilting ruler, cut the squares in half by cutting diagonally from one corner to corner.

Step 3a Cut the square in half again by cutting it diagonally from the other corner to corner.

Step 3b Open the quarters so the fabric is right side up. You now have four half quarter square triangles. You've made Patches 1 and 2, the small triangles.

Step 4 Make Patch 3 Now cut the two Fabric C squares in half by placing a quilting ruler from one diagonal corner to corner and use a rotary cutter to cut them in half.

Step 4a With right sides together, pair one of the QST halves with one of the half square triangle halves. Align them along their long edges. Stitch a 1/4 inch seam.

You have now made a 3 patch quarter square triangle. (Yes, the triangle for Patch 3 is a little bigger than the half quarter square triangle because we started with 4 squares all cut the same size.)

Repeat for remaining units.

Non-Mirror Image Quarter Square Triangles

Step 5 Open the 3 patch quarter square triangles with fabrics right sides up and press the seams toward the larger triangle, or open.

What we end up with are non-mirror image QSTs. Look carefully, all the units are the same, meaning that each of the three patches of each unit is in the same place.

Having all the patches in the same place is necessary if you want all your blocks to be exactly the same.

How To Square Up 3 Patch Quarter Square Triangles

Step 6 Square up the three patch QSTs from the center of the block where the two small triangles meet.

Divide the unfinished unit size in half (Column E in math chart above).

In this case, I'm making a 3 1/2 inch unfinished unit. Half of that is 1 3/4 inches.

So, on my quilting ruler I found the vertical and horizontal lines that correspond to this measurement (1 3/4 inches) and align them with the center of the block where the two small triangles meet (see where the drawn blue lines meet).

Using a rotary cutter, trim the unit along the right and top edges.

Step 7 Rotate the unit 180 degrees. Now you can align the bottom and left edges along the measurement lines that correspond to your unfinished unit size (Column F in math chart above). Here, that's 3 1/2 inches.

The center of your three patch QST should align with the measurement lines that are half of its unfinished size. (In this case, that's 1 3/4 inches.)

Be sure your unit is centered before trimming.  Align the center of the unit (where the 2 small triangles meet) with the measurement lines that are half its unfinished size (here, the 1 3/4 inch measurement lines).

Use a rotary cutter to trim the unit along the right and top edges and your 3 patch quarter square triangle is squared up!

Step 8 Trim any remaining 3 Patch quarter square triangles.

3 Patch Quarter Square Triangle Video

Here's a video on this technique by master quilter Deb Tucker. She calls these quarter square triangles Non Mirror Image Combination Units.